Telephone call-box system



Patented Aug. l, 1950 TELEPHONE CALL-Box SYSTEM f Ernest Frederick Bates, London, England, `assignor to International Standard Electric CorporatiomN ew York', N. Y.

i Application october 22, 1946, serial No. 704,959

In Great Britain October 5, 1945 Section 1, Public :Law 6910, August 8, 1946 Patent expires October 5, 1965 sclaims. (ci. 179-5)` This invention relates to telephone sets for use on single wire closed circuit telephone systems e; g. an ambulance call system or a 'ii're alarm system, or a police call system.

The object of the invention is to provide a call boxfor such a system inwhich, in spite of a fault in the circuit between the box and the station to be called, calls can be made without special operations on the part of the caller.

One feature of the invention comprises a cal1 box for a single-wire closed circuit telephone system in which a choice of circuit conditions is provided to suit particular line conditions and in which on the initiation of a call the correct circuit condition is automatically chosen in accordance with the existing line condition.

According to another feature of the invention a call box comprises testing means adapted to test for the existence of a fault, contacts operable on the initiation of a telephone call to render said testing means operative, and further `contacts controlled by said testing means and adapted to set up a connection to the called station unaffected by a detected fault.

The invention will be clearly understood from the following description of one'` embodiment thereof shown in the accompanying drawings, in which:

Figure 1 shows the mechanical arrangement of interacting contacts controlled by a latching relay and the door of a call box adapted to form part of a single wire closed circuit telephone system, in particular for an ambulance call box or a nre alarm system.

Figure 1A shows the box for housing the switching mechanism. J

, Figure 2 shows the circuit arrangement ofthe call-box.

Referring now to Figure l, a mounting plate I carries two` relay-type yokes 2, 3 of standard British post oiice type, each carrying an armature 5, 6 pivoted thereto by studs I3, I 4. A relay coil LR is mounted on the yoke 3, but no coil is provided on yoke 2, the armature 5 of which merely acts as a two-armed lever in a mechanical train to be described, and will hereafter be referred to as a lever.

A vertical stud I on yoke 3, carries a latching lever 9 with a latching extension I0. The lever 9 is urged by a spring 8 towards an extension plate I2 fixed to armature 6. An arm II fixed to lever 5 is shaped to co-operate with latch 9 and acts as an unlatching device as hereafter described.

A plate I5 xed to lever 5 by screw IE extends 2 across' armature 6 so that anti-clockwise movement of lever 5 will cause plate I5 to move armature 6 if in unoperated position.

A mountingplate vI9 xed to yoke 2 has pivoted to it at I8 a two-armed lever Il, the lower arm of which is connected `to plate I 5 by a spring 2l, while the upper arm is shaped at 20 to operate contact springs ds when the lever II rotates anti-clockwise, Contact springs cls are mounted on one side of yoke '2 out of range of lever 5, while two pairs of contact springs Trl, 2 are mounted on the other side of yoke 2 for operation by lever 5. Two pairs of contact springs ZTI, 2 are mounted on yoke 3 preferably one on each side for balanced operation by armature l.

Figure 2 shows the circuit arrangement of the contacts shown in Figure 1, the relay winding LR, together with the microtelephone instruments T, R, and switch-hook contacts gsl, gsZ.

The assembly shown in Figure l is mounted in an ambulance box a with the lower arm of lever I'I so positioned as to be moved to the right when the door b is closed, the door being hinged at c. Movement of lever I'I closes springs ds and through spring 2| and plate I5 operates lever 5 and armature A6 to operate their respective contacts Trl, 2 and ZTI, 2, 3, Figure 2, to the position shown. The microtelephone is on its cradle with switch hook contacts gsi, gs2 in the position shownwhile thebox is closed.`

When the box door b is opened, lever l1 moves clockwise, Figure l. The first result is that contacts ds open,` removing 9,` short circuit from relay LR. At this moment a circuit is completed for relay LR; line LA, contacts ZrI operated, contacts cs2,` gsI operated, LR, line LB. Relay LR acts` as a test relayfor the line condition as described below. After a moment sufficient for LR to operate, decrease of tension in spring 2l allowslever 5to` return to normal. If relay LR has not energisedarmature 6 will also return to normal. ,Release of `lever 5 allows its contacts rrI, M2 to close a short while after contacts ds open.

Further operation depends on condition of line.

No ,fault on, Zine Relay LR operates momentarily between the opening of contacts ds and closure of rrl. Latching lever 9 moves to bring its extension IIJ in front of arm I2, since it is no longer prevented by arm II on lever 5. Contacts lrl, '2, 3 therefore remain operated after LR is again shortcircuited by contacts rrI and thereby de-energised.

When the microtelephone is removed contacts gsi, cs2 change over, momentarily opening the line (or if desired inserting a resistance). The momentary opening of the line is a signal to the central station that a call is vbeing made. The microphone T and receiver R are then connected in the line via Zrl, earth being disconnected because contacts Zr3 are still open.

Earth fault on either side of box As in normal operation, LR will momentarily energise when the box is opened but in this case in a circuit between the earth fault and the central station. The box therefore "sets 'up a circuit identical with that formed in the normal case, but the circuit is energised between the earth fault and the central station instead of via the closed loop.

Open Zine on either side of bom There will .be no current on the line when con tacts ds open and in consequence relay LR will not energise so that contacts. Zri, 2, 3 will .return to normal as Well as rri, rr2.

Earth is Vnowconnected via rrii, Zr, gs2, and either gsi, rri, and the .li'ne IB; or Zr2 and the line LA; to the central station.

When the microtelephone is lifted, .contacts gsi, gs2 momentarilyopen Ythe earthed circuit .to signal the central station and finally the gravity switch contacts gsi, gs2 top, connect the .telephone set T. R. in the earthed circuit.

'Short circuit in 'the zboa:

As in the case of an open line, relay LR will not operate when the `box is opened and a circuit is set up from earth via theline, in rwhich the telephone circuit is nally inserted.

What is claimed is:

l. In a single wire closed circuit telephone system, a station connected in said circuit through two lines and including telephone receiver and transmitter yunits and an associated switch hook, means operable in order to utilize said station for initially vautomatically testing said lines for ground .and open circuit faults, .and means effective when at least one of said lines is free from faults and said switch hook is released for automatically connecting Vsaid units in the circuit over the latter line.

2. In a single wire closed circuit telephonesystem, the combination, as set forth inclaim I, in which the initial testing means includes 5a testing circuit and switch means for placing .the latter circuit in operation'for a limited .period prior tothe operation of 'the connecting means.

3. In a single .Wireclosed circuit telephone system, the combination, as set forth in `claim l, in which the station comprises a call-box which houses said units, vtesting means, and connecting o means, said box including a door, the initial testing means including a'test circuit and means including a switch 'for .placing the test circuit .in

4 operative condition for a limited period prior to the operation of the connecting means, and means for automatically operating said switch when the door is opened.

4.` In. a single wire closed circuit telephone system, the combination, as set forth in claim 1 in which the connecting means includes means for connecting said units in series between a ground- .ed'line .and the other line.

5. In a single wire closed circuit telephone system, the combination, as setforth in claim l including a ground connection, said connecting means including means operative when one of said lines is open to connect said units in series between said ground connection and the other line.

6. In a single wire closed circuit telephone system, a station connected in said circuit through two lines, a receiver and transmitter unit at said station, an electromagnet, means operable in order Yto utilize said station for 'establishing a circuit :between said lines through `the yelectromagnet for a limited period of time, switch means actuated by said electromagnet when `energized when said first-mentioned circuit is closed rand when one of said lines is grounded, to connect said unit in series with said lines, and actuated whensaid electromagnet is not energized by'reason of the fact that one of said .lines `is open, to connect said unit in series between the other line and ground.

7. In a single wire closed circuit telephone system, the combination, -as set forth in claim '5 in which the electromagnet is .normally :connected in series with said lines and the electromagnet connecting means includes, abypass 'cir-- cuit which short circuits the electromagnet, a switch inthe bypass circuit, and means for opening and then `closing said switch.

8. In a .single wire closed circuit telephone system, thecombination, as set forth .in 4claim 5, in which the connecting means vincludes an Yiarmature Vfor .the electromagnet, a switch 'connecting said unit to one lof the lineameans for closing said switch when saidarmature 'is-shifted by the electromagnet, .and latch means for retaining the switch in lclosed position after `the magnet is deenergized.

ERNEST FREDERICK BATES.

REFERENCES CITED The following references .are of record in vthe file of this patent: i

UNITED STATES PATENTS 

